Additive manufacture of porous ceramic proximal interphalangeal (PIP) joint implant: design and process optimization

Additive manufacturing (AM) is a promising method for fabricating customized and anatomically correct surgical implants. Advancement in design and the AM of joint replacement implants has mainly targeted implants for large joint replacement while progress in small joint replacements has been limited. This study describes a method for fabrication of porous biodegradable ceramic “templates” for use in preparing small joint implants such as the proximal interphalangeal (PIP) finger joint by combining powder-bed binder jetting (PBBJ) AM plus post-process sintering. A proposed PIP template design was selected using finite element analysis (FEA) to predict a suitable design for reliable fixation of the implant to host bone through bone ingrowth while providing necessary mechanical properties to avoid implant fracture during anticipated in vivo functional loading. Calcium polyphosphate (CPP) ceramic powder was selected for fabrication of the porous biodegradable ceramic templates intended to degrade in vivo in time to be replaced by bone while retaining a mature articular cartilage layer anchored to the intended joint bearing surface thereby achieving whole joint regeneration. For the AM build-up, density and mechanical strength of porous AM-made samples were optimized by varying the binder saturation level in the PBBJ process. Using the preferred design and processing conditions, PIP joint templates were made and subjected to preliminary fatigue testing to demonstrate survival under anticipated in vivo functional loading conditions. The study has demonstrated the potential of this novel approach for the preparation of implants for use in small digit joint regeneration.